In recent years, as a time-saving and a handling-reducing measure, blood sampling devices have been provided which make use of a double-ended needle. One end of this needle can be inserted into a vein and a previously evacuated and sterile displaceable sampling tube can be connected to the opposite end of the needle to receive the blood specimen.
Such specimen tubes can have a self-sealing closure at the mouth of the tube which can be pierced by the second end of the needle and communication can thereby be established between the evacuated interior of the sampling tube and the needle.
The closure can have a sealing membrane of an elastomeric material, e.g. a silicone rubber, which can be covered in turn by a flat, uniform thickness foil, e.g. of aluminum, which can be formed with a heat-sealable layer on its side turned toward the interior of the specimen tube.
A vacuum blood sampling tube of this type is described in German patent document--Open Application No. DE-OS 29 08 817. In that system, the closure is formed with a cap which is screwed onto the tube and has an opening spanned by the membrane through which a needle end can be inserted.
One problem with this specimen tube construction is that the mouth of the tube and the closure must be formed with mating screw threads and, of course, care must be taken upon threadedly interconnecting the cap and the tube that an effective seal is created. This can be a time-consuming process which cannot be readily carried out in an automated manner.
Access to the contents of the tube also requires unscrewing of the cap which is also a time-consuming process at the time of analysis and requires careful handling.
Perhaps a more significant disadvantage, however, is the fact that it is not possible to tell with such screw cap closures whether the interior of the sampling tube or its contents has been tampered with. Finally, when analysis is not to be carried out immediately, i.e. the tubes are to be stored for a comparatively long time, or the tubes are stored for a long time before they are used, problems are encountered because the cap materials are microporous and, indeed, vacuum may be lost so that the suction upon use may be insufficient.
In German patent document--Open Application No. DE-OS 22 43 593, a similar sampling tube is provided in which the closure is a metal cap which is clenched onto the tube end, much as a conventional bottle cap is applied. At its central portion, a circular crown part is provided and outwardly but connected thereto, the cap has an annular downwardly extending sleeve of inverted U-profile, the latter terminating in an upwardly bent edge. The central portion of the circular crown part is provided of reduced thickness so that it can be readily penetrated by the hollow needle. At least the inner surface of the metal cap, preferably its entire lower surface, is covered with a thin protective layer of polyvinyl chloride or some other vinyl composition to prevent the penetration of impurities into the interior of the tube. The seal is fixed to the outer surface of the metal cap and the mounting of the cap with its U-profile on the tube end is effected by means of hot melt materials such as polyamides to provide an adhesive bond between the abutting surfaces of the sleeve and the outer surface of the tube end.
With this arrangement, a bottle opener of conventional design may be used to remove the metal cap.
This conventional closure arrangement is not only relatively complex but, because it is composed of numerous parts, also suffers from lack of reliability and the need for relatively complex manipulation operations.
An improvement on the latter closure is described in Austrian Pat. No. 368 389. Here the closure comprises a foil of preferably uniform wall thickness and which is provided on one side with a heat-sealable layer forming a hermetic seal between the foil and the end faces of the tube, the foil being separated from the interior of the tube by this continuous heat-sealing layer.
In general, the use of heat-sealing foils, while satisfactory at least to a limited extent with blood sampling tubes, composed of synthetic resin materials, has not been fully satisfactory with glass tubes.